Analytical and experimental investigation determines the nature of oscillations and instabilities that occur in the flow of two-phase cryogenic fluids at both subcritical and supercritical pressures in heat exchangers. Test results with varying system parameters suggest certain design approaches with regard to heat exchanger geometry

Fleming, R. B.

Staub, F. W.

English

NASA Technical Reports Server

October 1969
	
Brief 69-10541 
NASA TECH BRIEF
--
NASA Tech Briefs are issued to summarize specific innovations derived from the U.S. space program, 
to encourage their commercial application. Copies are available to the public at 15 cents each 
from the Clearinghouse for Federal Scientific and Technical Information, Springfield, Virginia 22151. 
I 
Cryogenic Fluid Flow Instabilities in Heat Exchangers 
1 40
An analytical and experimental investigation was 
conducted to determine the nature of oscillations and 
instabilities that occur in the flow of two-phase cryo-
genic fluids at both subcritical and supercritical pres-
sures in heat exchangers. The objective was to obtain 
a fundamental understanding of the phenomena, with-, 
out regard to the design parameters of a particular 
heat exchanger configuration. 
The major experimental work was conducted with 
liquid nitrogen at subcritical pressures in an apparatus 
designed to provide data on the nature and rate of 
fluid (liquid and vapor) flow, heat transfer rates, and 
pressure drops. The heated test section of the appa-
ratus was constructed of glass tubing to permit visual 
observation of the flow. This section was designed for 
very high heat fluxes, possibly the highest heat fluxes 
which had previously been attained in any other simi-
lar transparent heated section. Heat was generated by 
passing an electric current through a conductive coat-
ing on the inside walls of the tubing. Seven separate 
lengths of glass tubing were used in the heated test 
section, so that the electrical power input could be 
varied in each of the seven lengths independently. The 
high heat fluxes ensured complete vaporization of the 
liquid in a single pass through the heated section. 
Various modes of coupling the heated section to the 
rest of the apparatus could be selected. 
The following four flow regimes were visually ob-
served in the tests: liquid jet flow, bubbly flow, an-
nular flow, and fog flow. It was found that the stability 
of the system depended both on the sequence in which 
these flows occurred along the heated tube and on 
the mode of coupling the liquid supply tank to the 
heated test section. In all cases, the highest amplitudes 
of flow oscillations occurred when the exit vapor
quality (i.e., ratio of vapor mass flow rate to total fluid 
mass flow rate) was the highest. It is believed that this 
effect is due to the flow regimes which existed under 
conditions of relatively high heat fluxes required for 
high exit vapor quality. Visual and photographic ob-
servation indicated that in most tests with inlet sub-
cooling, the area of wetted wall at the inlet remained 
fairly constant, even during oscillations. However, 
during oscillations, the flow regime in this inlet region 
changed periodically from bubbly, with clear liquid, 
to a churned-up mixture of liquid and vapor; and fog 
pulses at the same frequency as flow oscillations ap-
peared at the tube outlet. The results of the tests with 
varying system parameters suggest certain design 
approaches with regard to heat exchanger geometry 
which should increase system stability. 
Note: 
Requests for further information may be directed to: 
Technology Utilization Officer 
Marshall Space Flight Center 
Huntsville, Alabama 35812 
Reference: TSP69- 10541 
Patent status: 
Inquiries about obtaining rights for the commercial 
use of this invention may be made to NASA, Code GP, 
Washington, D.C. 20546. 
Source: R. B. Fleming and F. W. Staub of

General Electric Company

under contract to
Marshall Space Flight Center 
(MFS-20438) 
Category 02 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19690000512 2020-03-16T18:09:41+00:00Z


Cryogenic fluid flow instabilities in heat exchangers

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server